RADIATION-INDUCED OXIDATION AND ITS EFFEC T ON THE STRENGTH OF ULTRAORIENTED POLYETHYLENE FIBERS - KINETIC-MODEL

The oxidation and decrease in strength of ultraoriented high-molecular -weight polyethylene fibers were studied under air oxidation induced b y X-ray irradiation. The rate of accumulation of carbonyl groups at ra diation dose rate P less-than-or-equal-to Gy/s is proportional to P1/2 ; at P > 2 Gy/s it is proportional to P. The rate of decrease in the f iber strength can be described by a pseudo- first order equation with respect to the concentration of the most extended load-bearing tie mol ecules in amorphous regions of the polymer. The apparent rate constant is determined by the details of the oxidation mechanism, i.e., by the dependence of the rate of accumulation of carbonyl groups upon the ra diation dose rate (i.e., the rate of initiation). A structural-kinetic model is proposed which describes the decrease in the fiber strength during radiolysis in air. The model takes into account the peculiariti es of the structure and the oxidation kinetics of the oriented polymer .